1. Field of the Invention
The present invention relates to a fiber optics device used for fingerprint detection and the like.
2. Related Background Art
In a fingerprint detecting apparatus and the like, a fiber optics device is used as a means for converting the three-dimensional surface shape of a detection target into an optical image. As an example which practically uses such a fiber optics device as a fingerprint detecting apparatus, one described in Japanese Patent Laid-Open No. 7-174947 is known. In the fiber optics device of this reference, the direction of an optical axis of optical fibers constituting the fiber optics device is inclined by an inclination angle .theta. with respect to the incident angle and exit angle, as shown in FIG. 11 of the reference. A CCD is mounted on this exit surface. In this fiber optics device, the incident surface and the exit surface are formed to be inclined with respect to the direction of the optical axis, in order to prevent light from becoming incident on the fiber optics device directly from the external air. Also, the distance between a surface with which a finger as a detection target comes in contact (the incident surface of the fiber optics device) and the CCD is decreased, in order to decrease the size of the fingerprint detecting apparatus.
In the fiber optics device described above, since the light exit surface is also inclined with respect to the direction of the optical axis of the optical fibers, even if a fingerprint image is incident on the fiber optics device through the finger which has come in contact with the light-incident angle, light does not efficiently emerge to the external air from the image exit surface. Even if a CCD is mounted on the exit surface to change the exit characteristics, the quantity of light emerging from the exit surface is very small, and the image of a fingerprint to be detected tends to be dark accordingly.